The field of the invention is G protein-coupled receptors.
The rhodopsin-like G protein-coupled receptors, which are the single largest class of cell surface receptors, mediate a wide variety of essential physiological functions. For example, G protein-coupled receptors mediate the chemotactic movement of cells that ensures an adequate immune response, transmit the signals carried by hormones, and capture external stimuli such as the photons that strike the retina and the odorant molecules that strike the nasal epithelium (Probst et al., DNA Cell Biol. 11:1-20, 1992). All G protein-coupled receptors contain seven domains that traverse back and forth across the cell membrane; the proteinaceous loops that form between these transmembrane domains extend into the extracellular and intracellular spaces. The loops that extend extracellularly specifically interact with ligands, particularly peptide and protein ligands, and the intracellular loops interact with G proteins on the inner surface of the cell membrane, thereby beginning the biochemical cascade that transmits the extracellular signal to the interior of the cell. The third intracellular loop of many G protein-coupled receptors, particularly those that function as adrenergic and cholinergic receptors, is the largest intracellular structure, and is thought to be especially important for the interaction between the receptor and a G protein (Lefkowitz et al., Cold Spring Harbor Symposia Quant. Biol. 53:507-514, 1988).
The invention features a G protein-coupled receptor that has an enlarged extracellular loop between the fourth and fifth transmembrane domains. A nucleic acid encoding the receptor was isolated from a human granulocytic cell library and antibodies generated against the polypeptide revealed expression in a variety of tissues including heart, placenta, and lung. This antibody, or others that specifically bind the G protein-coupled receptor of the invention, can be used in the diagnosis of diseases or conditions that are associated with upregulation of the receptor, as occurs, for example, when hematopoietic cells differentiate. These diseases include inflammatory and neurological diseases, such as Alzheimer""s Disease. The nucleic acids, polypeptides, and antibodies described herein can also be used as therapeutic agents to treat these diseases by inhibiting the expression or activity of the receptor. They can also be used in the treatment of obesity.
Other features and advantages of the invention will be apparent from the detailed description and from the claims. Although materials and methods similar or equivalent to those described herein can be used in the practice or testing of the invention, the preferred materials and methods are described below.